Fibers, melt blown webs and other melt spun fibrous articles have been made from thermoplastic polymers, such as poly(propylene), polyamides, and polyesters. One common application of these fibers and fibrous articles are nonwoven fabrics and, in particular, in personal care products such as wipes, feminine hygiene products, baby diapers, adult incontinence briefs, hospital/surgical and other medical disposables, protective fabrics and layers, geotextiles, industrial wipes, and filter media. Unfortunately, the personal care products mades from conventional thermoplastic polymers are difficult to dispose of and are usually placed in landfills. One promising alternative method of disposal is to make these products or their components “flushable”, i.e., compatible with public sewerage systems. The use of water-dispersible or water-soluble materials also improves recyclability and reclamation of personal care products. The various thermoplastic polymers now used in personal care products are not inherently water-dispersible or soluble and, hence, do not produce articles that readily disintegrate and can be disposed of in a sewerage system or recycled easily.
The desirability of flushable personal care products has resulted in a need for fibers, nonwovens, and other fibrous articles with various degrees of water-responsivity. Various approaches to addressing these needs have been described, for example, in U.S. Pat. Nos. 6,548,592; 6,552,162; 5,281,306; 5,292,581; 5,935,880; and 5,509,913; U.S. patent application Ser. Nos. 09/775,312; and 09/752,017; and PCT International Publication No. WO 01/66666 A2. These approaches, however, suffer from a number of disadvantages and do not provide a fibrous article, such as a fiber or nonwoven fabric, that possesses a satisfactory balance of performance properties, such as tensile strength, absorptivity, flexibility, and fabric integrity under both wet or dry conditions.
For example, typical nonwoven technology is based on the multidirectional deposition of fibers that are treated with a resin binding adhesive to form a web having strong integrity and other desirable properties. The resulting assemblies, however, generally have poor water-responsivity and are not suitable for flushable applications. The presence of binder also may result in undesirable properties in the final product, such as reduced sheet wettability, increased stiffness, stickiness, and higher production costs. It is also difficult to produce a binder that will exhibit adequate wet strength during use and yet disperse quickly upon disposal. Thus, nonwoven assemblies using these binders may either disintegrate slowly under ambient conditions or have less than adequate wet strength properties in the presence of body fluids. To address this problem, pH and ion-sensitive water-dispersible binders, such as lattices containing acrylic or methacrylic acid with or without added salts, are known and described, for example, in U.S. Pat. No. 6,548,592 B1. Ion concentrations and pH levels in public sewerage and residential septic systems, however, can vary widely among geographical locations and may not be sufficient for the binder to become soluble and disperse. In this case, the fibrous articles will not disintegrate after disposal and can clog drains or sewer laterals.
Multicomponent fibers containing a water-dispersible component and a thermoplastic water non-dispersible component have been described, for example, in U.S. Pat. Nos. 5,916,678; 5,405,698; 4,966,808; 5,525,282; 5,366,804; 5,486,418. For example, these multicomponent fibers may be a bicomponent fiber having a shaped or engineered transverse cross section such as, for example, an islands-in-the-sea, sheath core, side-by-side, or segmented pie configuration. The multicomponent fiber can be subjected to water or a dilute alkaline solution where the water-dispersible component is dissolved away to leave the water non-dispersible component behind as separate, independent fibers of extremely small fineness. Polymers which have good water dispersibility, however, often impart tackiness to the resulting multicomponent fibers, which causes the fiber to stick together, block, or fuse during winding or storage after several days, especially under hot, humid conditions. To prevent fusing, often a fatty acid or oil-based finish is applied to the surface of the fiber. In addition, large proportions of pigments or fillers are sometimes added to water dispersible polymers to prevent fusing of the fibers as described, for example, in U.S. Pat. No. 6,171,685. Such oil finishes, pigments, and fillers require additional processing steps and can impart undesirable properties to the final fiber. Many water-dispersible polymers also require alkaline solutions for their removal which can cause degradation of the other polymer components of the fiber such as, for example, reduction of inherent viscosity, tenacity, and melt strength. Further, some water-dispersible polymers can not withstand exposure to water during hydroentanglement and, thus, are not suitable for the manufacture of nonwoven webs and fabrics.
Alternatively, the water-dispersible component may serve as a bonding agent for the thermoplastic fibers in nonwoven webs. Upon exposure to water, the fiber to fiber bonds come apart such that the nonwoven web loses its integrity and breaks down into individual fibers. The thermoplastic fiber components of these nonwoven webs, however, are not water-dispersible and remain present in the aqueous medium and, thus, must eventually be removed from municipal wastewater treatment plants. Hydroentanglement may be used to produce disintegratable nonwoven fabrics without or with very low levels (<5 wt %) of added binder to hold the fibers together. Although these fabrics may disintegrate upon disposal, they often utilize fibers that are not water soluble or water-dispersible and may result in entanglement and plugging within sewer systems. Any added water-dispersible binders also must be minimally affected by hydroentangling and not form gelatinous buildup or cross-link, and thereby contribute to fabric handling or sewer related problems.
A few water-soluble or water-dispersible polymers are available, but are generally not applicable to melt blown fiber forming operations or melt spinning in general. Polymers, such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylic acid are not melt processable as a result of thermal decomposition that occurs at temperatures below the point where a suitable melt viscosity is attained. High molecular weight polyethylene oxide may have suitable thermal stability, but would provide a high viscosity solution at the polymer interface resulting in a slow rate of disintegration. Water-dispersible sulfopolyesters have been described, for example, in U.S. Pat. Nos. 6,171,685; 5,543,488; 5,853,701; 4,304,901; 6,211,309; 5,570,605; 6,428,900; and 3,779,993. Typical sulfopolyesters, however, are low molecular weight thermoplastics that are brittle and lack the flexibility to withstand a winding operation to yield a roll of material that does not fracture or crumble. Sulfopolyesters also can exhibit blocking or fusing during processing into film or fibers, which may require the use of oil finishes or large amounts of pigments or fillers to avoid. Low molecular weight polyethylene oxide (more commonly known as polyethylene glycol) is a weak/brittle polymer that also does not have the required physical properties for fiber applications. Forming fibers from known water-soluble polymers via solution techniques is an alternative, but the added complexity of removing solvent, especially water, increases manufacturing costs.
Accordingly, there is a need for a water-dispersible fiber and fibrous articles prepared therefrom that exhibit adequate tensile strength, absorptivity, flexibility, and fabric integrity in the presence of moisture, especially upon exposure to human bodily fluids. In addition, a fibrous article is needed that does not require a binder and completely disperses or dissolves in residential or municipal sewerage systems. Potential uses include, but are not limited to, melt blown webs, spunbond fabrics, hydroentangled fabrics, dry-laid non-wovens, bicomponent fiber components, adhesive promoting layers, binders for cellulosics, flushable nonwovens and films, dissolvable binder fibers, protective layers, and carriers for active ingredients to be released or dissolved in water. There is also a need for multicomponent fiber having a water-dispersible component that does not exhibit excessive blocking or fusing of filaments during spinning operations, is easily removed by hot water at neutral or slightly acidic pH, and is suitable for hydroentangling processes to manufacture nonwoven fabrics. Other extrudable and melt spun fibrous materials are also possible.